The present invention relates to a brushed motor.
Conventionally, in a brushed motor, abnormal noise is generated by a force applied to a commutator from a brush during rotation, and the abnormal noise becomes a cause of noise, vibration, and the like. In particular, when the brushed motor is used in an on-board motor, which is required to be quiet, the noise or the like may become a problem.
A commutator has been proposed in which a plurality of segments (commutator pieces) arranged on an outer circumferential surface of the commutator have different circumferential widths so that undercuts (grooves) formed between adjacent segments are not located at equal intervals (e.g., Japanese Patent No. 3994010).
In the motor of Japanese Patent No. 3994010, a positive electrode brush and a negative electrode brush are arranged facing each other. Thus, the positive electrode and negative electrode brushes simultaneously traverse adjacent segments many times during each rotation produced by the motor. The large number of times the positive electrode and negative electrode brushes simultaneously traversing the adjacent segments for each rotation adversely affects the motor characteristics, increases the fluctuation width of the value of the current supplied to a winding, and increases rotation torque fluctuation, vibration, and the abnormal noise.